Aflatoxin B1 (AFB1), a potent hepatocarcinogen, undergoes metabolic activation via epoxidation. Interaction of activated AFB1 with cellular macromolecules especially with DNA is believed to be responsible for the initiation of cancer by this chemical. There is a wide difference in carcinogenicity of AFB1 between rats and hamsters and also in AFB1-DNA binding both in vivo and in vitro. Among various metabolic reactions that can modulate interaction of AFB1-epoxide, is a reaction of detoxification by reduced glutathione (GSH). The major emphasis of this program will be on AFB1-DNA interactions in liver tissues of both susceptible and resistant species. the specific aims of this project are: (1) To investigate both in vivo and in vitro whether GSH or GSH S-transferases play a major role in modulating the interaction of AFB1 with DNA, and (2) To investigate whether one or more of the specific GSH S-transferases react with the active intermediate of AFB1 thereby modulating AFB1-DNA interactions. These studies would involve whole animal, isolated hepatocytes, liver perfusion and subcellular experiments using rats, hamsters, mice, guinea pigs and rabbits. Hepatic GSH levels and GSH S-transferase activities will be regulated by administration of various chemicals to examine the kinetics of hepatic AFB1-DNA binding. Pretreatment of animals with diethyl maleate will lower hepatic GSH levels whereas cysteine treatment or low protein diet will increase GSH levels. Administration of phenobarbital or feeding of various dietary antioxidants (butylated hydroxyanisole and ethoxyquin) will increase GSH S-transferase activities. Diethyl maleate will also be administered to many of these pretreated animals to examine the kinetics of AFB1-DNA binding. Subcellular studies will include intact nuclei, microsomes and cytosol. Immunological techniques may help us to determine specificity and contributions of each of these various GSH S-transferases in AFB1 metabolism. The proposed studies would help us to understand the role of GSH S-tranferases in modulating AFB1-DNA interactions in livers of susceptible and resistant species. The long term objectives of this program are aimed at understanding the metabolic activation and inactivation steps involved in the carcinogenesis by AFB1 and other related mycotoxin, sterigmatocystin, in sensitive and resistant species.